<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 100px;
            height: 100px;
        }
        .divx1{
            background-color: red;
            position: relative;
            left: 50px;
            top:50px;
            z-index:-1;
        }
        .divx2{
            background-color: black;
            float: left;
        }
        .divx3{
            background-color: blue;
        }
    </style>
</head>
<body>
    <div class="divx1">div1</div>
    <div class="divx2"></div>
    <div class="divx3"></div>
</body>
</html>